Color processing device, image forming apparatus, and image forming system

ABSTRACT

A color processing device includes a color-data acquisition section, a conversion-relationship generation section, a correction-image-data generation section, and a conversion-relationship correction section. The color-data acquisition section acquires color data of a first image output by a first image forming device. In accordance with a first relationship and a second relationship, the conversion-relationship generation section generates a conversion relationship used for color adjustment performed to match a color of a second image to be output by a second image forming device on a basis of unadjusted image data with a color of the first image. The correction-image-data generation section generates, on a basis of the unadjusted image data, correction image data for correcting the conversion relationship. The conversion-relationship correction section performs correction of the conversion relationship on a basis of color data of correction images output by the second image forming device by using the correction image data.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 USC 119 fromJapanese Patent Application No. 2016-252621 filed Dec. 27, 2016.

BACKGROUND (i) Technical Field

The present invention relates to a color processing device, an imageforming apparatus, and an image forming system.

(ii) Related Art

In recent years, offset printing machines have been gradually andincreasingly replaced with on-demand digital printing machines in theprinting market. An example of an on-demand printer usage is reprinting.In reprinting, in some cases, an on-demand printer is used for a smallnumber of copies after an offset printing machine is used for a largenumber of copies, and in other cases, only an on-demand printer is usedwithout using an offset printing machine.

To adjust the colors of printed materials output in such reprinting tomatch the colors of printed materials output in the past, there is aneed to generate a color conversion profile through colorimetryperformed on color patches printed in the past and to output the printedmaterials using the same print output setting (such as a colorconversion profile setting) as those in the past.

SUMMARY

According to an aspect of the invention, there is provided a colorprocessing device including a color-data acquisition section, aconversion-relationship generation section, a correction-image-datageneration section, and a conversion-relationship correction section.The color-data acquisition section acquires color data of a first imageoutput by a first image forming device on a basis of image data. Theconversion-relationship generation section generates a conversionrelationship used for performing color adjustment. The conversionrelationship is generated in accordance with a first relationship thatis a relationship between unadjusted image data to undergo the coloradjustment and the color data of the first image and a secondrelationship regarding a second image forming device. The coloradjustment is performed to match a color of a second image to be outputby the second image forming device on a basis of the unadjusted imagedata with a color of the first image. The correction-image-datageneration section generates, on a basis of the unadjusted image data,correction image data for correcting the conversion relationship. Theconversion-relationship correction section performs correction of theconversion relationship on a basis of color data of correction imagesoutput by the second image forming device by using the correction imagedata.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the present invention will be described indetail based on the following figures, wherein:

FIG. 1 is a diagram illustrating an example of an overall configurationof an image forming system according to the exemplary embodiment;

FIG. 2 is a diagram illustrating the appearance of an image formingapparatus according to the exemplary embodiment;

FIG. 3 is a diagram illustrating the internal structure of the imageforming apparatus according to the exemplary embodiment;

FIG. 4 is a block diagram illustrating a signal processing system in acontroller;

FIG. 5 is a block diagram for explaining the functional configuration ofa color processing section;

FIGS. 6A, 6B, and 6C are diagrams and histograms illustrating a methodfor generating a region group;

FIG. 7 is a diagram for explaining a first example of Step 1 in which afirst-relationship generation section generates a first relationship;

FIG. 8 is a diagram for explaining a second example of Step 1 in whichthe first-relationship generation section generates the firstrelationship;

FIG. 9 is a diagram for explaining a third example of Step 1 in whichthe first-relationship generation section generates the firstrelationship;

FIGS. 10A, 10B, 10C, and 10D are diagrams for explaining Step 2 in whichthe first-relationship generation section generates the firstrelationship;

FIG. 11 is a diagram for explaining a correction image; and

FIG. 12 is a flowchart for explaining how the image forming apparatusperforms color adjustment for outputting an image having colors adjustedto match colors of another image forming apparatus.

DETAILED DESCRIPTION Overall Configuration of Image Forming System

An exemplary embodiment of the invention will be described in detailwith reference to the drawings.

FIG. 1 is a diagram illustrating an example of an overall configurationof an image forming system according to the exemplary embodiment.

An image forming system S illustrated in FIG. 1 includes an imageforming apparatus 1 and an image forming apparatus 2.

Each of the image forming apparatuses 1 and 2 is a printing mechanismthat forms an image on a medium (recording medium) on the basis of imagedata and uses at least one type of a color material. The image datarepresents an image for, for example, a print job transmitted from auser. The image data may be data in a raster image format or datadescribed in a page description language (PDL).

Each of the image forming apparatuses 1 and 2 uses, for example, anelectrophotographic system in the exemplary embodiment. After theprinting on a medium, each of the image forming apparatuses 1 and 2outputs the medium as a printed material to the outside. FIG. 1illustrates a case where the image forming apparatus 1 forms an image G1(first image) on a sheet of paper (paper sheet) P1 and outputs the papersheet P1 and where the image forming apparatus 2 forms an image G2(second image) on a paper sheet P2 and outputs the paper sheet P2.

The image forming apparatus 2 includes at least an image reading device100 that reads an image, and the image reading device 100 reads theimage G1 formed on the paper sheet P1. This will be described in detaillater.

Image Forming Apparatus Overview

An overview of the image forming apparatuses 1 and 2 will be described.The image forming apparatuses 1 and 2 basically have the sameconfiguration, and the image forming apparatus 2 will hereinafter bedescribed taken as an example.

FIG. 2 is a diagram illustrating the appearance of the image formingapparatus 2 according to the exemplary embodiment. FIG. 3 is a diagramillustrating the internal structure of the image forming apparatus 2according to the exemplary embodiment.

The image forming apparatus 2 includes the image reading device 100 thatreads the image of a document and an image recording device 200 that isan example of an image forming device that forms an image on a medium onthe basis of image data. The image recording device 200 functions as afirst image forming device in the image forming apparatus 1 andfunctions as a second image forming device in the image formingapparatus 2. The image forming apparatus 2 further includes a userinterface (UI) 300 and a controller 900. The UI 300 receives useroperation input and displays various pieces of information to the user.The controller 900 controls overall operations of the image formingapparatus 2.

The image reading device 100 is an example of an image reading deviceand is disposed in an upper portion of the image forming apparatus 2.The image recording device 200 is disposed under the image readingdevice 100 and has the controller 900 incorporated in the imagerecording device 200. The user interface 300 is disposed on the sidecloser to the user in the upper portion of the image forming apparatus2, that is, the side, closer to the user, of an image reading section110 (described later) of the image reading device 100.

The image reading device 100 will first be described.

The image reading device 100 includes the image reading section 110 thatreads the image of a document and a document transport section 120 thattransports the document to the image reading section 110. The documenttransport section 120 and the image reading section 110 are respectivelydisposed in an upper portion and a lower portion of the image readingdevice 100.

The document transport section 120 includes a document tray 121 thataccommodates the document and a document discharge section 122 to whichthe document transported from the document tray 121 is discharged. Thedocument transport section 120 transports the document from the documenttray 121 to the document discharge section 122.

The image reading section 110 includes a platen glass 111, a lightirradiating unit 112, a light guide unit 113, and an imaging lens 114.The light irradiating unit 112 radiates light L onto a read surface(image surface) of the document. The light guide unit 113 guides thelight L reflected from the read surface of the document. The imaginglens 114 forms an optical image of the light L guided by the light guideunit 113. The image reading section 110 also includes a detector 115 andan image processing section 116. The detector 115 includes photoelectricconversion elements, such as a charge coupled device (CCD) image sensor,which photoelectrically convert the image of the light L formed throughthe imaging lens 114. The detector 115 detects the formed optical image.The image processing section 116 is electrically connected to thedetector 115 and receives electric signals obtained by the detector 115.

The image reading section 110 reads not only the image of the documenttransported by the document transport section 120 but also the image ofthe document placed on the platen glass 111.

The image recording device 200 will be described.

The image recording device 200 includes an image forming section 20, amedium supply section 60, a medium discharge section 70, and a reversingsection 80. The image forming section 20 forms an image on a medium. Themedium supply section 60 supplies the image forming section 20 with apaper sheet P. The medium discharge section 70 discharges the papersheet P on which the image forming section 20 forms the image. Thereversing section 80 turns over the paper sheet P having a surface onwhich the image forming section 20 forms the image. The reversingsection 80 transports the paper sheet P again to the image formingsection 20.

The image forming section 20 includes four image forming units 21 (21Y,21M, 21C, and 21K) for yellow (Y), magenta (M), cyan (C), and black (K)that are arranged parallel to and a predetermined distance away fromeach other. Each image forming unit 21 includes a photoconductor drum22, a charger 23 that uniformly charges the surface of thephotoconductor drum 22, and a developer 24 that develops and makesvisible an electrostatic latent image formed by laser radiated by anoptical system unit 50 (described later) by using predeterminedcolor-component toner. The image forming section 20 also includes tonercartridges 29Y, 29M, 29C, and 29K for respectively supplying color tonerto the developers 24 of the image forming units 21Y, 21M, 21C, and 21K.

The image forming section 20 includes the optical system unit 50 belowthe image forming units 21Y, 21M, 21C, and 21K, the optical system unit50 radiating a laser beam onto the photoconductor drums 22 of therespective image forming units 21Y, 21M, 21C, and 21K. The opticalsystem unit 50 includes semiconductor laser (not illustrated), amodulator (not illustrated), a polygon mirror (not illustrated) fordeflective scanning of the laser beam emitted from the semiconductorlaser, a glass window (not illustrated) through which the laser beampasses, and a frame (not illustrated) for hermetically enclosing thecomponents.

In addition, the image forming section 20 includes an intermediatetransfer unit 30, a second transfer unit 40, and a fixing device 45. Theintermediate transfer unit 30 transfers color toner images respectivelyformed on the photoconductor drums 22 of the image forming units 21Y,21M, 21C, and 21K onto an intermediate transfer belt 31 in such a manneras to superpose the color toner images on each other. The secondtransfer unit 40 transfers, onto a paper sheet P, a toner image formedon the intermediate transfer unit 30 through the superposition. Thefixing device 45 heats and presses the toner image formed on the papersheet P to thereby fix the toner image on the paper sheet P.

The intermediate transfer unit 30 includes the intermediate transferbelt 31, a drive roller 32 that drives the intermediate transfer belt31, and a tension roller 33 that provides the intermediate transfer belt31 with a predetermined tension. The intermediate transfer unit 30 alsoincludes multiple (four in the exemplary embodiment) first transferrollers 34 and a backup roller 35. Each first transfer roller 34 facesthe corresponding photoconductor drum 22 across the intermediatetransfer belt 31 and is provided to transfer the toner image formed onthe photoconductor drum 22 onto the intermediate transfer belt 31. Thebackup roller 35 faces a second transfer roller 41 (described later)across the intermediate transfer belt 31.

The intermediate transfer belt 31 is stretched around multiple rotarymembers such as the drive roller 32, the tension roller 33, the firsttransfer rollers 34, the backup roller 35, and driven rollers 36. Theintermediate transfer belt 31 is driven to be rotated at a predeterminedspeed in the arrow direction by the drive roller 32 rotated by a drivemotor (not illustrated). The intermediate transfer belt 31 is made of,for example, rubber or resin.

The intermediate transfer unit 30 also includes a cleaning device 37that removes remaining toner and the like on the intermediate transferbelt 31. The cleaning device 37 removes the remaining toner, paperpowder, and the like from the surface of the intermediate transfer belt31 having undergone the toner image transfer process.

The second transfer unit 40 includes the second transfer roller 41 thatis disposed at the second transfer location and that performs secondtransfer of an image onto the paper sheet P by pressing the intermediatetransfer belt 31 against the backup roller 35. The second transferroller 41 and the backup roller 35 that faces the second transfer roller41 across the intermediate transfer belt 31 define the second transferlocation where the toner image transferred onto the intermediatetransfer belt 31 is transferred onto the paper sheet P.

The fixing device 45 uses a heat fixing roller 46 and a pressure roller47 to heat and press the image (toner image) having undergone the secondtransfer performed by the intermediate transfer unit 30. The fixingdevice 45 thereby fixes the image onto the paper sheet P.

The medium supply section 60 includes medium containers 61, a feedroller 62, a transport path 63, and transport rollers 64, 65, and 66.Each medium container 61 contains media on which images are to berecorded. The feed roller 62 is used to feed paper sheets P contained inthe medium container 61. Each paper sheet P fed with the feed roller 62is transported through the transport path 63. The transport rollers 64,65, and 66 are arranged along the transport path 63 and are used totransfer the paper sheet P fed with the feed roller 62 to the secondtransfer location.

The medium discharge section 70 includes a first stacking tray 71 and asecond stacking tray 72. The first stacking tray 71 is disposed abovethe image forming section 20, and media on which the image formingsection 20 forms images are stacked on the first stacking tray 71. Thesecond stacking tray 72 is disposed between the first stacking tray 71and the image reading device 100, and media on which the image formingsection 20 forms images are stacked on the second stacking tray 72.

The medium discharge section 70 includes a transport roller 75 and aswitching gate 76. The transport roller 75 is disposed downstream of thefixing device 45 in a transport direction and used to transport thepaper sheet P having the toner image fixed thereon. The switching gate76 is disposed downstream of the transport roller 75 in the transportdirection and performs switching between the first stacking tray 71 andthe second stacking tray 72 that are targets for discharging the papersheet P. The medium discharge section 70 also includes a first dischargeroller 77 disposed downstream of the switching gate 76 and used fordischarging the paper sheet P transported toward the first stacking tray71 (rightwards in FIG. 3) having undergone the switching performed bythe switching gate 76 as one of the targets of discharging the paper P.The medium discharge section 70 also includes a transport roller 78 anda second discharge roller 79. The transport roller 78 is disposeddownstream of the switching gate 76 and used for transporting the papersheet P toward the second stacking tray 72 (upwards in FIG. 3) havingundergone the switching performed by the switching gate 76 as the othertarget of discharging the paper sheet P, and the second discharge roller79 is used for discharging the paper sheet P transported with thetransport roller 78 to the second stacking tray 72.

The reversing section 80 includes a reversing path 81 that is disposedat the side of the fixing device 45 and through which the paper sheet Pis transported, the paper sheet P being turned over by rotating thetransport roller 78 in a direction opposite from the direction ofdischarging the paper sheet P to the second stacking tray 72. Thereversing path 81 is provided with multiple transport rollers 82arranged along the reversing path 81. The paper sheet P transported withthe transport rollers 82 is transported again to the second transferlocation by using the transport rollers 82.

The image recording device 200 also includes a body frame 11 and ahousing 12. The body frame 11 directly or indirectly supports the imageforming section 20, the medium supply section 60, the medium dischargesection 70, the reversing section 80, and the controller 900. Thehousing 12 is attached to the body frame 11 and forms an outer surfaceof the image forming apparatus 2.

The body frame 11 includes an image-reading-device supporting section 13including the switching gate 76, the first discharge roller 77, thetransport roller 78, the second discharge roller 79, and othercomponents and extending vertically to support the image reading device100 on one lateral end portion of the image forming apparatus 2. Theimage-reading-device supporting section 13 together with a part, of thebody frame 11, farther from the user supports the image reading device100.

The image recording device 200 also includes a front covering 15 that ispart of the housing 12, that is disposed on a side, of the image formingsection 20, closer to the user, and that is attached to the body frame11 to be openable.

By opening the front covering 15, the user may replace any one of theintermediate transfer unit 30 and the toner cartridges 29Y, 29M, 29C,and 29K of the image forming section 20 with new one.

The user interface 300 is, for example, a touch panel. When the touchpanel is used as the user interface 300, various pieces of informationsuch as image forming setting for the image forming apparatus 2 aredisplayed on the touch panel. The user touches the touch panel toperform operations of inputting the image forming setting and the like.

Example of Functional Configuration of Controller

FIG. 4 is a block diagram illustrating a signal processing system in thecontroller 900. Note that FIG. 4 illustrates functions related to signalprocessing that are selected from functions of the controller 900.

The controller 900 includes a data acquisition section 91, a rasterizingsection 92, a color adjustment section 93, a color processing section94, a raster-image adjustment section 95, a halftone processing section96, and an image-data output section 97. The data acquisition section 91acquires image data generated for outputting an image from the imagerecording device 200. The rasterizing section 92 generates a rasterimage from the acquired image data. The color adjustment section 93performs color adjustment on CMYK data. The color processing section 94generates a profile for the color adjustment to be performed by thecolor adjustment section 93. The raster-image adjustment section 95adjusts the raster image converted by the color adjustment section 93.The halftone processing section 96 performs halftone processing. Theimage-data output section 97 outputs the image data having undergonecolor conversion processing to the image recording device 200.

In the exemplary embodiment, the data acquisition section 91 firstreceives PDL data serving as the image data.

The rasterizing section 92 converts the PDL data acquired by the dataacquisition section 91 into raster data for each pixel. At this time,the rasterizing section 92 also converts the raster data including red,green, and blue (RGB) data into raster data including CMYK data. Forexample, after generating the raster data, the rasterizing section 92converts the RGB data included in the raster data into XYZ color valuesthat are device-independent, thereafter converts the XYZ color valuesinto pieces of CMYK data that represent colors reproduced by the imagerecording device 200 (colors of toner as color materials that are cyan(C), magenta (M), yellow (Y), and black (K)), and outputs the pieces ofCMYK data. The pieces of CMYK data are a piece of color C data, a pieceof color M data, a piece of color Y data, and a piece of color K datathat are separated on a per color basis.

The rasterizing section 92 outputs the raster image including thegenerated CMYK data to the color processing section 94. The data is datayet to be adjusted by the color adjustment section 93 and is to undergocolor adjustment. In the exemplary embodiment, this is referred to as“unadjusted image data”.

The color adjustment section 93 performs the color adjustment on theimage to be formed by the image recording device 200. The coloradjustment section 93 performs the color adjustment on the CMYK data soas to match the colors with desired colors to be output by the imagerecording device 200 in accordance with the CMYK data. Note that in theimage forming apparatus 2, the color adjustment section 93 is also usedso as to perform the color adjustment for outputting an image havingcolors adjusted to match those of a printed material output by the imageforming apparatus 1. This will be described later.

The color adjustment is a process for converting, for example, CMYK datainto C_(in)M_(in)Y_(in)K_(in) data into C_(out)M_(out)Y_(out)K_(out)data (pieces of data C_(in), M_(in), Y_(in) and K_(in) into pieces ofdata C_(out), M_(out), Y_(out), and K_(out)). In the exemplaryembodiment, the conversion is performed by using a so-called “devicelink profile” in which the C_(in)M_(in)Y_(in)K_(in) data is directlyconverted into the C_(out)M_(out)Y_(out)K_(out) data in the same CMYKcolor space as for the C_(in)M_(in)Y_(in)K_(in) data. In the exemplaryembodiment, theC_(in)M_(in)Y_(in)K_(in) data is not converted into datain other color spaces such as an L*a*b* color space. The coloradjustment section 93 stores the device link profile and applies theC_(in)M_(in)Y_(in)K_(in) data to the device link profile to therebyperform the color adjustment.

In the exemplary embodiment, the color adjustment section 93 functionsas a color adjustment device that performs color adjustment on an imageto be formed by the image recording device 200 of the image formingapparatus 2. The device link profile is an example of a conversionrelationship and may be generated as, for example, a four-dimensionallook up table (LUT). In the exemplary embodiment, data having undergonethe color adjustment performed by the color adjustment section 93 isreferred to as “adjusted image data”.

The color processing section 94 generates a device link profile used forthe color adjustment performed by the color adjustment section 93. Thecolor processing section 94 will be described in detail later. The colorprocessing section 94 is an example of a color processing device. Thecolor processing section 94 is also an example of aconversion-relationship generation device that generates a conversionrelationship (device link profile) used for the color adjustmentperformed by the color adjustment section 93.

The raster image adjustment section 95 performs γ conversion, finenessprocessing, halftone processing, or the like on the C_(out)M_(out)Y_(out)K_(out) data input from the color adjustment section 93 andperforms various adjustments to obtain a better quality of an imageoutput from the image recording device 200.

The halftone processing section 96 performs halftone processing on theadjusted image data by using dither mask processing that uses a dithermask having a predetermined threshold array in the main and sub scandirections. The adjusted image data is thereby expressed with, forexample, binary values, not multiple values.

The image-data output section 97 outputs, to the image recording device200, the adjusted image data having undergone the image processing suchas the color conversion processing.

Color Processing Section

The color processing section 94 of the image forming apparatus 2 will bedescribed in detail. A case where the color processing section 94performs the color adjustment to output an image having colors adjustedto match the colors of a printed material output by the image formingapparatus 1 will be described.

The color processing section 94 generates a device link profile used forperforming the color adjustment as described above.

FIG. 5 is a block diagram for explaining the functional configuration ofthe color processing section 94.

The color processing section 94 includes an unadjusted-image-dataacquisition section 941, a region-group extraction section 942, acolor-data acquisition section 943, a first-relationship generationsection 944, a second-relationship acquisition section 945, asecond-relationship memory 946, a conversion-relationship generationsection 947, a correction-image-data generation section 948, acorrection determination section 949, a first-relationship correctionsection 950, and a conversion-relationship correction section 951.

The unadjusted-image-data acquisition section 941 acquires unadjustedimage data from the rasterizing section 92.

The region-group extraction section 942 extracts specific regions in animage as a region group on the basis of the unadjusted image data. Theregion group is composed of extracted regions that are set to determinea color difference between printed materials respectively output by theimage forming apparatus 2 and the image forming apparatus 1. The colordifference is acquired to adjust the colors of the printed material tobe output by the image forming apparatus 2 to match those output by theimage forming apparatus 1. The region-group extraction section 942extracts the region group from the unadjusted image data that is theraster data acquired by the unadjusted-image-data acquisition section941.

The region-group extraction section 942 also generates, as region-groupinformation, information regarding the extracted region group. Theregion-group information includes information used for identifying theextracted regions forming the region group. For example, theregion-group information includes location information or imageinformation regarding the extracted regions. The region-groupinformation will be described in detail later.

The color-data acquisition section 943 acquires color data (first colordata) of an image G1 (first image) output by the image recording device200 of the image forming apparatus 1. To acquire the color data, forexample, the printed material having the image G1 is read by using theimage reading device 100 of the image forming apparatus 2. Specifically,the image reading section 110 of the image reading device 100 reads thecolors of the printed material and generates the color data. Examples ofusable color data include L*a*b* values as device-independent data. TheL*a*b* values are defined using the L*a*b* color space (also referred toas a CIELAB color space). In addition, the L*a*b* color space isexpressed using a Cartesian coordinate color space having axes of thelightness L* and chromaticities a* and b* indicating hue.

Note that the CCD provided to the image reading section 110 generallyreads an image on the basis of RGB data; however, after the reading, theimage reading section 110 may convert the RGB data into L*a*b* data byusing a multi-dimensional table corresponding to the readingcharacteristics of the CCD and may thereby output color data having theL*a*b* values. The multi-dimensional table may use, for example,International Color Consortium (ICC) profiles generated in accordancewith the reading characteristics of the CCD.

The first-relationship generation section 944 generates a firstrelationship between the unadjusted image data and the color data (firstcolor data) of the image G1 acquired by the color-data acquisitionsection 943.

The first relationship is a relationship (CMYK-L*₁a*₁b*₁) between theCMYK data included in the unadjusted image data and the L*a*b* data thatis the color data (first color data) (hereinafter, the first color datais also referred to as “L*₁a*₁b*₁ data”). A method for generating afirst relationship will be described in detail later.

The second-relationship acquisition section 945 acquires a secondrelationship regarding the image recording device 200 of the imageforming apparatus 2, the second relationship corresponding to the firstrelationship for the image forming apparatus 2, the second relationshipbeing between the unadjusted image data and the color data acquired fromthe image forming apparatus 2.

The second relationship is a relationship (CMYK-L*₂a*₂b*₂) between theCMYK data and the L*a*b* data that is the color data (second color data)(hereinafter, the second color data is also referred to as “L*₂a*₂b*₂data”). The second relationship has been stored in thesecond-relationship memory 946, and the second-relationship acquisitionsection 945 acquires the second relationship from thesecond-relationship memory 946.

The second relationship is generated in advance and stored in thesecond-relationship memory 946. To generate a second relationship, amethod in the related art may be used. For example, an image of colorpatches covering the full color gamut of the image recording device 200of the image forming apparatus 2 is printed. The colors of the printedimage are subsequently measured by using a colorimeter or anotherdevice, and color data is acquired. The color data thus acquired is thesecond color data (L*₂a*₂b*₂ data). The unadjusted image data forprinting the image of the color patches is correlated with the secondcolor data, and the second relationship is thereby acquired.

The conversion-relationship generation section 947 generates, on thebasis of the first and second relationships, a conversion relationshipfor performing color adjustment on an image G2 (second image) to beoutput from the image recording device 200 of the image formingapparatus 2 to match the colors of the image G2 with the colors of animage G1 (first image).

Specifically, the L*a*b* data (L*_(l)a*₁b*_(l) data) in the firstrelationship is compared with the L*a*b* data (L*₂a*₂b*₂ data) in thesecond relationship. A relationship in the CMYK data between the firstand second relationships at the time when the L*_(l)a*₁b*_(l) data andthe L*₂a*₂b*₂ data match is generated. Specifically, the firstrelationship represents a relationship between the CMYK data that is theunadjusted image data and the colors of the image G1 printed by theimage forming apparatus 1 when the CMYK data is input. Note that theterm “to match” denotes “to match completely” or “to be similar to apredetermined degree”. The second relationship represents a relationshipbetween the CMYK data and the colors of the image G2 printed by theimage forming apparatus 2 when the CMYK data is input. Even if the sameCMYK data is input, the image G1 and the image G2 do not have the samecolors because the apparatuses have different characteristics. Incontrast, the conversion relationship represents the relationship of theCMYK data of the same colors between the images respectively printed bythe image forming apparatuses 1 and 2. Hence, the CMYK data that is theunadjusted image data is converted by using the conversion relationship,and the image forming apparatus 2 prints an image by using the convertedCMYK data. The image forming apparatus 2 naturally prints the image G2having the same colors as those of the image G1 printed by the imageforming apparatus 1. The use of the conversion relationship enables thecolor adjustment through which the image forming apparatus 2 prints aprinted material in such a manner that the colors of the printedmaterial are adjusted to match the colors of the printed material outputfrom the image forming apparatus 1. The conversion relationship isincluded in the four-dimensional LUT and is the device link profile, asdescribed above. The device link profile is transmitted to the coloradjustment section 93, and the color adjustment section 93 uses thedevice link profile to perform the color adjustment of the image formedby the image recording device 200.

However, the color adjustment using the conversion relationshipgenerated by the above-mentioned method does not have high accuracy insome cases. In the exemplary embodiment, the correction-image-datageneration section 948, the correction determination section 949, thefirst-relationship correction section 950, and theconversion-relationship correction section 951 are provided to enhancethe conversion relationship accuracy.

The correction-image-data generation section 948 generates, on the basisof unadjusted image data, correction image data for correcting theconversion relationship. The correction image data is data of an imageused for correction (correction image). The correction image is aso-called color patch. This will be described in detail later. The imageforming apparatus 2 prints the correction image on the basis of thecorrection image data. The printed correction image has undergone thecolor adjustment performed by the conversion-relationship generationsection 947 in accordance with the conversion relationship describedabove. The color patch is measured with a colorimeter or another device,and the color data of the correction image may thereby be acquired.Instead of measuring the color patch with the colorimeter or anotherdevice, the method described with reference to the color-dataacquisition section 943 may be used to acquire the color data.

In the exemplary embodiment, a user who uses a personal computer (PC)does not correct the conversion relationship by using data of an imageintended to be printed by using the image forming apparatus 2. Instead,correction images in which multiple color patches are respectivelyarranged are generated. The color patches have a highly uniform color asthe representative color of regions forming a region group extracted bythe region-group extraction section 942. This enables the color data tobe acquired and consequently enables the conversion relationship to becorrected with higher accuracy.

The color data of each correction image is acquired by the color-dataacquisition section 943 and then transmitted to the correctiondetermination section 949.

The correction determination section 949 obtains a color differencebetween the color data (first color data) of the image G1 (first image)and the corresponding color data of the correction image. The correctiondetermination section 949 determines, on the basis of the colordifference, whether the conversion relationship generated by theconversion-relationship generation section 947 needs to be corrected.Specifically, a predetermined threshold is provided for thedetermination by the correction determination section 949. If the colordifference is equal to or smaller than the threshold, the correctiondetermination section 949 determines that the conversion relationshipdoes not need to be corrected. In contrast, if the color difference islarger than the threshold, the correction determination section 949determines that the conversion relationship needs to be corrected. Inother words, if the conversion relationship generated by theconversion-relationship generation section 947 enables the coloradjustment to be performed accurately, the color difference is equal toor smaller than the threshold, and thus the conversion relationship doesnot need to be corrected. In contrast, if the conversion relationshipgenerated by the conversion-relationship generation section 947 does notenable the color adjustment to be performed accurately, the colordifference is larger than the threshold, and thus the conversionrelationship needs to be corrected.

When the conversion relationship needs to be corrected, thefirst-relationship correction section 950 corrects the firstrelationship. Specifically, the first-relationship correction section950 superposes the color difference on the first relationship generatedby the first-relationship generation section 944 and generates acorrected first relationship having the color difference reflectedthereon.

The conversion-relationship correction section 951 corrects theconversion relationship in accordance with the first relationshipcorrected by the first-relationship correction section 950.Specifically, the conversion-relationship correction section 951regenerates a conversion relationship in accordance with the correctedfirst relationship generated by the first-relationship correctionsection 950 and the second relationship by the same method as that usedby the conversion-relationship generation section 947.

In this case, it may also be said that the conversion-relationshipcorrection section 951 corrects the conversion relationship on the basisof the color data of the correction image output by the image recordingdevice 200 of the image forming apparatus 2 by using the correctionimage data.

A corrected device link profile that is the corrected conversionrelationship is transmitted to the color adjustment section 93 in thesame manner as the above-described device link profile. The coloradjustment section 93 then uses the corrected device link profile toperform the color adjustment on the image to be formed by the imagerecording device 200.

It is preferable to repeat the correction of the conversion relationshipuntil the color difference between the color data (first color data) ofthe image G1 (first image) and the corresponding color data of thecorrection image satisfies a predetermined condition. That is, feedbackis performed to enhance the accuracy of the conversion relationship.Specifically, the correction is repeated until the correctiondetermination section 949 determines that the conversion relationshipdoes not need to be corrected because the color difference is equal toor smaller than the threshold. In addition, the correction determinationsection 949 may be configured not to perform further correction if aneffect of color difference reduction is no longer obtained even thoughthe color difference is larger than the threshold. Alternatively, thecorrection determination section 949 may be configured not to performfurther correction if the conversion relationship is performed apredetermined number of times even though the color difference is largerthan the threshold.

In the case where the correction of the conversion relationship isrepeated, the image forming apparatus 2 prints a correction image inaccordance with the previously corrected conversion relationship, andthe color data of the correction image is acquired again. Since thecorrection image does not change, the correction image data firstgenerated by the correction-image-data generation section 948 may beused without any additional processing. The correction determinationsection 949 then determines whether the corrected conversionrelationship needs to be corrected. If the corrected conversionrelationship needs to be corrected, the first-relationship correctionsection 950 again corrects the first relationship, and theconversion-relationship correction section 951 again corrects theconversion relationship. Thereafter, this is repeated until thecorrection determination section 949 determines that the conversionrelationship does not need to be corrected. Region-group Information

The region-group information generated by the region-group extractionsection 942 will be described.

The extracted regions forming the region group are regions having colorswhich are substantially uniform (hereinafter, referred to as uniformregions). Regions having substantially the same color signal in suchuniform-color regions are selected as the extracted regions. As long asthe uniform-color regions have substantially the same color signal, noneof the uniform-color regions do not have to be the same size.

FIGS. 6A, 6B, and 6C are diagrams and histograms illustrating a methodfor generating a region group.

The region-group extraction section 942 sets scan rectangles of apredetermined size as illustrated in FIG. 6A and scans the raster imageon the basis of the scan rectangles. The region-group extraction section942 generates histograms of pixel values in each scan rectangle.

FIG. 6B illustrates examples of the histograms of a scan rectangle.

FIG. 6B illustrates a case where CMYK values in a raster image areconverted into color values in an L*C*H* color space in which colors arerepresented using lightness, chroma, and hue and where histograms forlightness (L*), chroma (C*), and hue (H*) are generated. The horizontalaxes respectively represent lightness (L*), chroma (C*), and hue (H*),and the vertical axes each represent the number of pixels as frequency.

A range having the highest frequency peak in the histogram is determinedas a dominant-color range. FIG. 6B illustrates the ranges each havingthe highest frequency peak as the dominant-color ranges. A regionincluded in the dominant-color range in the scan rectangle is referredto as a dominant-color region. If a percentage of the area (the numberof pixels) of the dominant-color region relative to the area (the numberof pixels) of the scan rectangle is equal to or higher than apredetermined threshold, and if color distribution of the pixels in thedominant-color region is equal to or lower than a predeterminedthreshold, the scan rectangle is selected as an extracted region. Thedominant-color region of an adjacent scan rectangle is also checked. Ifthe colors in the dominant-color regions are identical, the scanrectangles are coupled to each other. The processing is repeated for thescan rectangles arranged in succession, and such scan rectangles aregrouped as a larger unit than a single scan rectangle. Thedominant-color regions thus grouped are set as extracted regions. Theextracted regions have an amorphous outline as illustrated, for example,in FIG. 6C.

A predetermined threshold for the height of a peak in FIG. 6B may beprovided. If the height of a peak is lower than the threshold, it isdesirable not to determine a range including the peak as thedominant-color range and not select the scan rectangle including theregion as the extracted region.

The region-group extraction section 942 generates the region-groupinformation. The region-group information includes the locationinformation regarding the extracted regions. The location informationincludes, for example, an X upper-left-corner-of-circumscribed-rectanglecoordinate, a Y upper-left-corner-of-circumscribed-rectangle coordinate,a circumscribed-rectangle width, a circumscribed-rectangle height, andbitmap information.

The X and Y upper-left-corner-of-circumscribed-rectangle coordinates arerespectively the X and Y coordinates of the upper left corner of therectangle indicated by a dotted line including the extracted regions asillustrated in FIG. 6C. The circumscribed-rectangle width is a width Wof the circumscribed rectangle, and the circumscribed-rectangle heightis a height H of the circumscribed rectangle H. According to theinformation, the location of the circumscribed rectangle isidentifiable.

The bitmap information is binary image information having values of 1indicating pixels belonging to the extracted regions in thecircumscribed rectangle and 0 indicating the other pixels. In this case,areas indicated by 1 in the binary image are the extracted regions, andareas indicated by 0 are the other regions. The location of eachextracted region in the circumscribed rectangle is thus identifiable.

The region-group information also includes information regarding theminimum values (L*_(min), C*_(min), and H*_(min)) and the maximum values(L*_(max), C*_(max) and H*_(max)) of the lightness (L*). the chroma(C*), and the hue (H*) of the dominant-color region. The range of thecolors in the extracted region is thereby identifiable.

Method for Generating First Relationship

How the first-relationship generation section 944 generates the firstrelationship will be described. The first relationship is hereingenerated in two steps of Step 1 and Step 2.

FIG. 7 is a diagram for explaining a first example of Step 1 in whichthe first-relationship generation section 944 generates a firstrelationship. FIG. 7 illustrates the first example as a method A.

First, Part (a) of FIG. 7 illustrates CMYK data that is unadjusted imagedata. The CMYK data is converted into L*C*H* data illustrated in Part(b) of FIG. 7. The region-group information illustrated in Part (c) ofFIG. 7 is subsequently referred to, and the L^(*)C^(*)H^(*) dataregarding pixels in each extracted region is extracted as illustrated inPart (d) of FIG. 7. This is performed in such a manner that the locationof each extracted region is first identified according to the locationinformation included in the region-group information and that theextracted region is further identified on the basis of the minimumvalues (L*_(min), C*_(min), and H*_(min)) and the maximum values(L*_(max), C*_(max), and H*_(max)) of the L*, C*, and H* values in theextracted region. This enables identification of the location of theextracted region even if there is a discrepancy in region locationbetween the unadjusted image data and the color data (first color data).

The L*C*H* data of each pixel in the extracted region is subsequentlyrestored to the CMYK data as illustrated in Part (e) of FIG. 7. Further,the pieces of CMYK data of the respective pixels in the extracted regionare averaged, and the average is used as the CMYK data of each extractedregion illustrated in Part (f) of FIG. 7.

In contrast, Part (g) of FIG. 7 illustrates the L*_(l)a*₁b*_(l) datathat is color data (first color data). The processing in Parts (h) to(j) of FIG. 7 is performed in the same manner as in Parts (b) to (d) ofFIG. 7. The L*C*H* data of each pixel in the extracted region issubsequently restored to the L*_(l)a*₁b*_(l) data as illustrated in Part(k) of FIG. 7. Further, the pieces of L*_(l)a*₁b*_(l) data of therespective pixels in the extracted region are averaged, and the averageis used as the L*_(l)a*₁b*_(l) data of each extracted region illustratedin Part (1) of FIG. 7.

Subsequently, the CMYK data of each extracted region illustrated in Part(f) of FIG. 7 and the L*_(l)a*₁b*_(l) data of each region in the regiongroup illustrated in Part (1) of FIG. 7 are correlated with each other.

FIG. 8 is a diagram for explaining a second example of Step 1 in whichthe first-relationship generation section 944 generates the firstrelationship. FIG. 8 illustrates the second example as a method B.

The processing in Parts (a) to (f) of FIG. 8 is performed in the samemanner as in Parts (a) to (f) of FIG. 7.

Part (g) of FIG. 8 is identical to Part (g) of FIG. 7 and illustratesthe L*_(l)a*₁b*_(l) data that is color data (first color data). In thismethod, however, as illustrated in Part (h) of FIG. 8, theL*_(l)a*₁b*_(l) data is extracted in the same region as in Part (e) ofFIG. 8. Subsequently, the pieces of L*_(l)a*₁b*_(l) data of therespective pixels in each extracted region are averaged, and the averageis used as the L*_(l)a*₁b*_(l) data of the extracted region illustratedin Part (i) of FIG. 8.

FIG. 9 is a diagram for explaining a third example of Step 1 in whichthe first-relationship generation section 944 generates the firstrelationship. FIG. 9 illustrates the third example as a method C.

The processing in Parts (d) to (i) of FIG. 9 is performed in the samemanner as in Parts (g) to (1) of FIG. 7.

Part (a) of FIG. 9 is identical to Part (a) of FIG. 7 and illustratesthe CMYK data that is unadjusted image data. In this method, however, asillustrated in Part (b) of FIG. 9, the CMYK data is extracted in thesame region as in Part (h) of FIG. 9. Subsequently, the pieces of theCMYK data of the respective pixels in each extracted region areaveraged, and the average is used as the CMYK data of the extractedregion illustrated in Part (c) of FIG. 9.

In the method A described with reference to FIG. 7, the L*C*H* data inPart (b) of FIG. 7 does not exactly match the L*C*H* data in Part (h) ofFIG. 7 even though the L*C*H* data in Part (b) of FIG. 7 and the L*C*H*data in Part (h) of FIG. 7 are acquired on the basis of the samelocation, and the method A thus results in a slight discrepancytherebetween. Each extracted region is extracted as described above byusing the minimum values (L*_(min), C*_(min), and H*_(min)) and themaximum values (L*_(max), C*_(max), and H*_(max)) of the L*, C*, and H*values. Accordingly, the extracted region in Parts (d) and (e) of FIG. 7does not exactly match the extracted region in Parts (j) and (k) of FIG.7 due to the discrepancy in the L*C*H* data, and this causes a locationdiscrepancy between the extracted regions. As long as the discrepancy inL*C*H* data is not large, the location discrepancy between the extractedregions stays within a small range; however, a large discrepancy in theL*C*H* data causes a large location discrepancy between the extractedregions, so that the accuracy of the first relationship might bedeteriorated.

In the method B described with reference to FIG. 8, the extracted regionin Part (e) of FIG. 8 exactly matches the extracted region in Part (h)of FIG. 8. Accordingly, in a case where there is a large discrepancy inthe L*C*H* data, the method B is likely to have higher accuracy of thefirst relationship than the method A. The same holds true for the methodC.

Nevertheless, colors in unadjusted image data do not generally cover thefull color gamut of the image forming apparatus 1. Accordingly, Step 1generally results in a small number of first relationships(CMYK-L*₁a*₁b*₁), and a sufficiently large number of first relationshipsto generate a high accuracy conversion relationship are not acquired inmany cases. Hence, processing for covering the shortage is performed inStep 2.

FIGS. 10A, 10B, 10C, and 10D are diagrams for explaining Step 2 in thegeneration of first relationships performed by the first-relationshipgeneration section 944.

The first-relationship generation section 944 applies the unadjustedimage data and the acquired color data (first color data) of the imageG1 to first relationship candidates prepared in advance in a wider colorgamut than the color gamut of pieces of color data (first color data)and subsequently performs matching on the unadjusted image data and theacquired color data with a corresponding one of the first relationshipcandidates.

FIG. 10A is a conceptual diagram illustrating the first relationshipcandidates prepared in advance.

FIG. 10A illustrates the first relationship (CMYK-L^(*) ₁a^(*) ₁b^(*) ₁)candidates prepared in advance in the full color gamut (a rhombic area)of the image forming apparatus 1.

FIG. 10B illustrates the first relationships (CMYK-L^(*) ₁a^(*) ₁b^(*)₁) acquired in Step 1. In this case, the first relationshipsrespectively have six pieces of data.

In the exemplary embodiment, the pieces of unadjusted image data andacquired color data (first color data) in FIG. 10B are applied to thefirst relationship candidates in FIG. 10A and are then merged, asillustrated in FIG. 10C.

The pieces of data in FIG. 10A, however, do not match the pieces of datain FIG. 10B, and not only application but also matching is thusperformed. For example, one or more pieces of data in FIG. 10A in aEuclidean distance shorter than a predetermined Euclidean distance froma corresponding one of the pieces of data in FIG. 10B are removed.Alternatively, a weighting is set on the basis of a Euclidean distancefrom each piece of data in FIG. 10B to the corresponding piece of datain FIG. 10A, and the pieces of data in FIG. 10B are weighted.

FIG. 10D is a graph illustrating a weighting w set as a Euclideandistance d.

In FIG. 10D, the horizontal axis represents the Euclidean distance d,the vertical axis represents the weighting w, and a relation w=1/(1+d)is set.

In this case, the weighting w thus set is decreased as the Euclideandistance d from the corresponding piece of distance in FIG. 10B isdecreased. For example, in a case where the Euclidean distance d is 0,the weighting w is 0. This case is equivalent to a case where thecorresponding piece of data in FIG. 10A does not exist. The weighting wthus set is increased as the Euclidean distance d from the correspondingpiece of distance in FIG. 10B is increased. If the Euclidean distance dis longer than a predetermined Euclidean distance d₀, the weighting wis 1. The case where the weighting w is 1 is equivalent to a case wherethe corresponding piece of data is weighted with no weighting w.

FIG. 10C illustrates locations D1, D2, and D3 of the pieces of data inFIG. 10A that are to be removed or weighted.

In this manner, the first-relationship generation section 944 covers theshortage of the first relationships in Step 1 and generates firstrelationships (CMYK-L*₁a*₁b*₁) that cover the full color gamut of theimage forming apparatus 1. That is, in Step 1, on the basis of the colordata (first color data) of the image G1 acquired from the region group,the first-relationship generation section 944 generates a firstrelationship that partially covers the color gamut of the image formingapparatus 1 as a relationship between the unadjusted image data and thecolor data (first color data). In Step 2, the first-relationshipgeneration section 944 generates a first relationship that covers thefull color gamut of the image forming apparatus 1 by applying the firstrelationship that partially covers the color gamut of the image formingapparatus 1 to the first relationship candidates prepared in advance andby performing the matching. Note that “performing matching” hereinincludes merging pieces of data and performing adjustment using theweightings of the pieces of data as described above.

Note that colors in the unadjusted image data in the first relationships(CMYK-L*₁a*₁b*₁) acquired in Step 1 might cover the full color gamut ofthe image forming apparatus 1. In this case, there is no need to performthe processing in Step 2 described above. The first-relationshipgeneration section 944 may thus be provided with a judgment section thatjudges the necessity of the processing in Step 2, and whether to performthe processing in Step 2 may be judged in accordance with a result ofthe judgment performed by the judgment section. To judge this, forexample, the color gamut of the image forming apparatus 1 is dividedinto regions, and frequency distribution indicating how many pieces ofdata in FIG. 10B are included in each region is calculated. A judgmentis made on the basis of whether a region exhibiting low frequency ispresent.

The first relationship candidates illustrated in FIG. 10A are desirablyclose to the first relationships acquired in Step 1 in FIG. 10B. A largediscrepancy therebetween causes deterioration of color reproductionaccuracy or continuity near a boundary between the relationships eventhough the aforementioned matching is performed.

Hence, multiple first relationship candidates may be prepared in advancefor each first relationship acquired in Step 1, and one of thecandidates may be selected as the first relationship candidate for thefirst relationship. In other words, one of the first relationshipcandidates that is closest to the first relationship acquired in Step 1is selected. In this case, the first-relationship generation section 944may be provided with, for example, a setting section that selects one ofthe first relationship candidates and sets the first relationshipcandidate.

For example, if it is known that the image G1 has been output under thecondition close to Japan Color 2011, a first relationship candidateusing the Japan Color 2011 condition may be included in the multiplefirst relationship candidates. A first relationship candidate using astandard and frequently used condition may also be included. A firstrelationship candidate having a typical condition used for image formingapparatuses sold in the past may also be included. A larger number offirst relationship candidates may also be automatically generated.

Correction Image

A correction image output by the image recording device 200 of the imageforming apparatus 2 will be described on the basis of correction imagedata generated by the correction-image-data generation section 948.

FIG. 11 is a diagram for explaining a correction image.

Correction images GH are color patches as described above and are eachformed into a rectangle, for example, as illustrated in FIG. 11.

In the exemplary embodiment, the correction-image-data generationsection 948 generates correction image data on the basis of unadjustedimage data generated by the rasterizing section 92 and does not useunadjusted image data included in the first relationship candidatesdescribed above. In other words, the unadjusted image data included inthe first relationship candidates is used to cover the full color gamutof the image forming apparatus 1 and does not directly represent thecolor reproducibility of the image recording device 200 of the imageforming apparatus 1. In contrast, the unadjusted image data generated bythe rasterizing section 92 directly represents the color reproducibilityof the image recording device 200 of the image forming apparatus 1, andthe use of this leads to enhancement of the accuracy of the coloradjustment performed by the image recording device 200 of the imageforming apparatus 2.

Correction image data for forming each correction image GH is the sameas the unadjusted image data of the regions forming the region groupextracted by the region-group extraction section 942. Thecorrection-image-data generation section 948 generates the correctionimage data to arrange each correction image GH in the location of theregions forming the region group extracted by the region-groupextraction section 942.

This results in formation of the correction image GH in accordance withthe unadjusted image data of the regions forming the region groupextracted by the region-group extraction section 942. In addition, thecorrection image GH is formed in the location of the regions forming theregion group extracted by the region-group extraction section 942.Specifically, the location of each correction image GH illustrated inFIG. 11 corresponds to the location of the corresponding regions formingthe region group extracted by the region-group extraction section 942.This enables the color adjustment to be performed to address a colordifference caused by variations in color observed on one plane.

Although the correction images GH are of the same size in the example inFIG. 11, the sizes of the respective correction images GH are notlimited to the same size. The correction images GH may be of differentsizes. For example, the size of each correction image GH may be changedin accordance with the size of the regions forming the region groupextracted by the region-group extraction section 942. In other words,the larger the extracted regions, the larger the correspondingcorrection image GH. The smaller the extracted regions, the smaller thecorresponding correction image GH. Note that the shape of eachcorrection image GH may be changed in accordance with the shape of theregions. Color Adjustment Performed by Image Forming Apparatus 2

Subsequently, how the image forming apparatus 2 performs coloradjustment for outputting an image G2 having colors adjusted to matchthose of the image forming apparatus 1 will be described.

FIG. 12 is a flowchart for explaining how the image forming apparatus 2performs the color adjustment for outputting the image G2 having colorsadjusted to match colors of the image forming apparatus 1.

Hereinafter, description is given by using FIGS. 5 and 12.

First, a printed material on which an image G1 output by the imageforming apparatus 1 is printed and image data used for printing theprinted material are prepared (step S101).

The image reading device 100 of the image forming apparatus 2subsequently reads the image G1 (first image) (step S102).

The color data (first color data) of the image G1 read by the imagereading device 100 is transmitted to the color processing section 94 ofthe controller 900, and the color-data acquisition section 943 of thecolor processing section 94 acquires the color data (first color data)(step S103).

In contrast, the image data of the image G1 formed by the image formingapparatus 1 is processed by the rasterizing section 92. Theunadjusted-image-data acquisition section 941 then acquires unadjustedimage data from the rasterizing section 92 (step S104).

The region-group extraction section 942 extracts specific regions in theimage as a region group on the basis of the acquired unadjusted imagedata (step S105). To extract the region group, for example, the methoddescribed with reference to FIGS. 6A to 6C is used.

The first-relationship generation section 944 generates a firstrelationship that is a relationship between the unadjusted image dataand the color data (first color data) acquired by the color-dataacquisition section 943 (step S106). To generate the first relationship,for example, one of the methods described with reference to FIGS. 7 to10D is used.

The second-relationship acquisition section 945 acquires a secondrelationship stored in the second-relationship memory 946 (step S107).

The conversion-relationship generation section 947 generates, on thebasis of the first and second relationships, a conversion relationshipfor the image recording device 200 of the image forming apparatus 2 toperform the color adjustment (step S108).

The conversion-relationship generation section 947 outputs theconversion relationship as a device link profile to the color adjustmentsection 93 (step S109).

The correction-image-data generation section 948 generates, on the basisof the unadjusted image data, correction image data for correcting theconversion relationship (step S110).

The correction-image-data generation section 948 outputs the correctionimage data, and the image recording device 200 of the image formingapparatus 2 prints correction images GH as illustrated in FIG. 11 on apaper sheet P2 (step S111).

The image reading device 100 of the image forming apparatus 2subsequently reads each correction image GH (step S112).

Color data of the correction image GH read by the image reading device100 is transmitted to the color processing section 94 of the controller900, and the color-data acquisition section 943 of the controller 900acquires color data of the correction image GH (step S113).

The correction determination section 949 acquires a color differencebetween the color data (first color data) of the image G1 (first image)and the corresponding color data of the correction image GH (step S114).

The correction determination section 949 determines whether the colordifference is equal to or smaller than the predetermined threshold (stepS115).

If the color difference is equal to or smaller than the predeterminedthreshold as a result of the determination (Yes in step S115), theseries of steps is terminated.

If the color difference is larger than the predetermined threshold (Noin step S115), the first-relationship correction section 950 correctsthe first relationship (step S116).

The conversion-relationship correction section 951 further corrects theconversion relationship in accordance with the corrected firstrelationship (step S117).

The conversion-relationship correction section 951 outputs theconversion relationship as a device link profile to the color adjustmentsection 93 (step S118). The processing thereafter returns to step S111.

The color adjustment section 93 performs conversion of the unadjustedimage data by using the device link profile so as to adjust the colorsof the image G2 to match the colors of the image G1. The colors of theimage G2 to be output by the image forming apparatus 2 thereby match thecolors of the image G1 output by the image forming apparatus 1.

The image reading device 100 is incorporated in the image formingapparatus 2 in the example described above in detail but may beseparately provided as an independent apparatus.

Likewise, the controller 900 is incorporated in the image formingapparatus 2, but the function of the color processing section 94 of thecontroller 900 may be independently provided. Operations of the functionmay be performed by, for example, a PC, a tablet terminal, a smartphone,or another apparatus. In this case, the function of the color processingsection 94 may be implemented by software (a program) run on such anapparatus.

Further, the image forming apparatuses 1 and 2 basically having the sameconfiguration have been described above in detail by taking, as anexample, an apparatus that forms an image by using anelectrophotographic system. However, the configuration is not limited tothat of the apparatus. An apparatus capable of forming an image on amedium (recording medium) by using an inkjet system or an offsetprinting system other than the electrophotographic system and outputtingthe medium may be used.

In the example described above in detail, the unadjusted image data toundergo the color adjustment is data acquired after the rasterizingsection 92 rasterizes image data acquired by the data acquisitionsection 91 but is not limited to the data resulting from therasterization. The unadjusted image data may be data resulting fromanother type of image processing. Note that some apparatuses have thesame unadjusted image data as the image data.

The exemplary embodiment has heretofore been described. The technicalscope of the invention is not limited to the scope of the exemplaryembodiment. From the description of the scope of claims, it is apparentthat the technical scope of the invention includes various modificationsand improvements made to the exemplary embodiment.

The foregoing description of the exemplary embodiment of the presentinvention has been provided for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Obviously, many modificationsand variations will be apparent to practitioners skilled in the art. Theembodiment was chosen and described in order to best explain theprinciples of the invention and its practical applications, therebyenabling others skilled in the art to understand the invention forvarious embodiments and with the various modifications as are suited tothe particular use contemplated. It is intended that the scope of theinvention be defined by the following claims and their equivalents.

What is claimed is:
 1. A color processing device comprising: acolor-data acquisition section that acquires color data of a first imageoutput by a first image forming device on a basis of image data; aconversion-relationship generation section that generates a conversionrelationship used for performing color adjustment, the conversionrelationship being generated in accordance with a first relationshipthat is a relationship between unadjusted image data to undergo thecolor adjustment and the color data of the first image and a secondrelationship regarding a second image forming device, the coloradjustment being performed to match a color of a second image to beoutput by the second image forming device on a basis of the unadjustedimage data with a color of the first image; a correction-image-datageneration section that generates, on a basis of the unadjusted imagedata, correction image data for correcting the conversion relationship;and a conversion-relationship correction section that performscorrection of the conversion relationship on a basis of color data ofcorrection images output by the second image forming device by using thecorrection image data.
 2. The color processing device according to claim1, wherein the correction image data is data of the correction images inwhich a plurality of color patches having a highly uniform color arerespectively arranged.
 3. The color processing device according to claim1, wherein the first relationship is generated by applying theunadjusted image data and the acquired color data of the first image toa first relationship candidate prepared in advance and by performingmatching on the unadjusted image data and the color data with the firstrelationship candidate.
 4. The color processing device according toclaim 1, further comprising: a region-group extraction section thatextracts regions in an image as a region group on a basis of the imagedata, wherein the first relationship is generated on a basis of colordata of the regions of the first image, the color data being acquiredfrom the region group.
 5. The color processing device according to claim4, wherein the correction-image-data generation section generates thecorrection image data to arrange each correction image in a location ofthe regions forming the region group extracted by the region-groupextraction section.
 6. The color processing device according to claim 1,wherein the conversion-relationship correction section repeats thecorrection of the conversion relationship until a color differencebetween the color data of the first image and corresponding color dataof each correction image satisfies a predetermined condition.
 7. Animage forming apparatus comprising: a second image forming device thatforms an image on a recording medium on a basis of image data, thesecond image forming device being different from a first image formingdevice that forms an image on a recording medium on a basis of the imagedata; a color adjustment device that performs color adjustment on theimage to be formed by the second image forming device; and aconversion-relationship generation device that generates a conversionrelationship that is used by the color adjustment device to perform thecolor adjustment, the conversion-relationship generation deviceincluding a color-data acquisition section that acquires color data of afirst image output by the first image forming device on the basis of theimage data, a conversion-relationship generation section that generatesthe conversion relationship used for performing the color adjustment,the conversion relationship being generated in accordance with a firstrelationship that is a relationship between unadjusted image data toundergo the color adjustment and the color data of the first image and asecond relationship regarding the second image forming device, the coloradjustment being performed to match a color of a second image to beoutput by the second image forming device on a basis of the unadjustedimage data with a color of the first image, a correction-image-datageneration section that generates, on a basis of the unadjusted imagedata, correction image data for correcting the conversion relationship,and a conversion-relationship correction section that performscorrection of the conversion relationship on a basis of color data of acorrection image output by the second image forming device by using thecorrection image data.
 8. An image forming system comprising: a firstimage forming device that forms an image on a recording medium on abasis of image data; a second image forming device that forms an imageon a recording medium on a basis of the image data; a color adjustmentdevice that performs color adjustment on the image to be formed by thesecond image forming device; and a conversion-relationship generationdevice that generates a conversion relationship that is used by thecolor adjustment device to perform the color adjustment, theconversion-relationship generation device including a color-dataacquisition section that acquires color data of a first image output bythe first image forming device on the basis of the image data, aconversion-relationship generation section that generates the conversionrelationship used for performing the color adjustment, the conversionrelationship being generated in accordance with a first relationshipthat is a relationship between unadjusted image data to undergo thecolor adjustment and the color data of the first image and a secondrelationship regarding the second image forming device, the coloradjustment being performed to match a color of a second image to beoutput by the second image forming device on a basis of the unadjustedimage data with a color of the first image, a correction-image-datageneration section that generates, on a basis of the unadjusted imagedata, correction image data for correcting the conversion relationship,and a conversion-relationship correction section that performscorrection of the conversion relationship on a basis of color data of acorrection image output by the second image forming device by using thecorrection image data.